A dialysis system is used as a substitute for the natural kidney functions of a human body. The dialysis system cleans the blood of the natural accumulation of bodily wastes by separating the wastes from the blood outside or extracorporeally of the body. The separated wastes are discharged and the cleansed blood is returned to the body.
The dialysis system consists of a dialysis machine, a dialyzer, a disposable blood tubing set and a supply of chemicals for producing a dialysate solution used within the dialyzer. The dialyzer is used with the dialysis machine to separate the wastes from the blood. The dialyzer includes a porous membrane located within a closed housing which effectively separates the housing into a blood compartment and a dialysate or filtrate compartment. The blood removed from the patient flows through the disposable blood tubing set and the blood side of the dialyzer. The dialysate solution prepared from the chemicals is passed through the dialysate side of the dialyzer. The wastes from the blood pass through the membrane by osmosis, ionic transfer or fluid transport into the dialysate and, depending upon the type of dialysis treatment, desirable components from the dialysate may pass in the opposite direction through the membrane and into the blood. The transfer of the wastes into the dialysate cleanses the blood while allowing the desired components from the dialysate to enter the bloodstream.
The transfer of blood between the patient and the dialyzer occurs within a disposable blood tubing set. The blood tubing set and the dialyzer represent a closed extracorporeal path through which the patient's blood travels. The blood tubing set includes an arterial line connected to an arterial reservoir for drawing blood from a patient, a venous line connected to a venous reservoir for returning blood to the patient, and a number of other lines for connecting a pump and the dialyzer between the arterial and venous reservoirs. Before the blood tubing set and the dialyzer can be used in a dialysis treatment, both must be primed with a sterile saline solution to remove air from the extracorporeal circuit. Once primed, the saline solution is recirculated through the blood tubing set and the dialyzer to produce a stabilized flow and remove additional trapped air from within the extracorporeal circuit. The priming and recirculating process also serves to clean the dialyzer and flush the dialyzer membrane of any debris or chemicals remaining from a prior use.
If a patient reuses the same dialyzer for subsequent dialysis treatments, that dialyzer must be cleaned with a disinfectant or sterilant solution. However, the sterilant itself must be cleaned from the dialyzer prior to each dialysis treatment. Such a cleaning procedure effectively takes place when the dialyzer undergoes the priming and recirculating process discussed above. During priming, the dialyzer is flushed with saline solution which removes a majority of the sterilant. Additionally, during recirculation of the saline solution, the dialysis machine can be commanded to remove or "pull" a predetermined flow of saline directly from the dialyzer. This predetermined flow corresponds to "pulling off" a predetermined amount of fluid (or weight) from a patient during dialysis, and is commonly referred to as "ultrafiltration." Removing saline by ultrafiltration during recirculation of the saline solution thus allows the remaining sterilant within the dialyzer to be removed as it mixes with the saline. The saline that is removed by ultrafiltration is replenished from a saline source connected to the extracorporeal circuit so that no additional air is added to the extracorporeal circuit during recirculation.
Current dialysis machines require that the priming and recirculation steps be undertaken separately, and further require an operator to alter the configuration of the blood tubing set and the saline source upon the conclusion of the priming step and before the start of the recirculation step. For example, a typical priming sequence on a conventional dialysis machine requires that the operator connect the outlet of the dialysis machine (i.e., the venous line) to a saline source and then operate the dialysis machine in reverse to fill the extracorporeal circuit with saline. Initially, the priming solution passes through the dialyzer and, in light of the reverse flow, exits the extracorporeal circuit through the dialysis machine's input line (i.e., the arterial line) which the operator connects to a waste basin or drain to dispose of the priming solution. The initial priming solution is discarded because it may contain relatively large quantities of sterilant flushed from the dialyzer when the dialyzer is sterilized and reused following a previous dialysis treatment.
Once the blood tubing set and dialyzer have been primed, the operator must disconnect the venous and arterial lines of the blood tubing set from the saline source and waste basin, respectively, and then connect the venous and arterial lines together (i.e., short circuiting the patient). The operator then switches the dialysis machine from its reverse operation and operates the machine normally to recirculate the saline solution through the extracorporeal circuit. The operator must further connect the saline source to a different portion of the circuit so that additional saline may be supplied to replace the saline removed by ultrafiltration during recirculation.
Thus, the processes of priming and recirculating conventional dialysis machines requires significant attention from a trained operator. The operator must configure the machine at several points during the process. Of the two separate procedures, recirculating the saline requires more time than initially priming the circuit with saline. Thus, if the operator is distracted after beginning the priming procedure and is unable to immediately return to the machine to reconfigure the blood tubing set and begin the recirculation procedure, a significant delay may be experienced in preparing the machine for the next patient. The potential for delay is significantly increased in a hospital or clinical setting where an operator or nurse must set up a number of different dialysis machines over the course of a day and where there is a greater possibility of distraction.
Additionally, while a skilled nurse or technician would be unlikely to make a mistake during the set up of a dialysis machine, the often hectic atmosphere of a hospital or clinic increases the chances of an error in machine set-up. For example, an operator may become distracted while the dialysis machine is recirculating and pulling saline from the dialyzer. If the saline source (e.g., a typical saline bag) were to run dry while the operator was distracted, the machine would continue to pull saline through the dialyzer and would tend to empty the extracorporeal circuit of saline, thereby allowing air to enter the circuit. Once a significant amount of air is introduced into the circuit, the priming and recirculation process must be started over at the cost of machine down-time and a new bag of sterile saline solution. Furthermore, although hospitals and dialysis clinics typically establish specific parameters for the set up and use of dialysis machines, these specific parameters may not be adhered to by an operator when setting up a particular dialysis machine. For example, inconsistent priming or recirculation procedures (such as too little saline during priming or running the machine for too short a time during recirculation) may be followed when the operator is distracted during the course of setting up the dialysis machine or when a hospital or clinic hires a new operator that is unfamiliar with the established set-up parameters.
These and other considerations have contributed to the evolution of the present invention which is summarized below.